The invention constitutes an improvement on the medical stone extracting device disclosed in U.S. Pat. No. 5,906,622, which is manufactured in accordance with U.S. Pat. No. 7,210,210 and sold commercially under the trade mark “N-Gage” by Cook Urological. The disclosure of the '622 and '210 patents are hereby incorporated by reference into the present specification. The “N-Gage” device includes a stone extracting unit mounted on the distal end of an elongated cannula operated by a hand piece mounted on the proximal end of the cannula. The stone extracting unit itself comprises three annularly arranged elongated tubular elements fixed together at their proximal ends to a distal end of a fixed component of the cannula, the proximal end of which is connected to a fixed component of the hand piece. The manually movable component of the hand piece is connected to the proximal end of a movable component of the cannula which extends through the fixed component of the cannula. The distal end of the movable cannula component is connected to move three elongated wire elements of the stone extracting unit. The three elongated wire elements extend through the three fixed tubular elements so that their free end portions extend outwardly of the free ends of the tubular elements. The free ends of the three wire elements are then connected in fixed relation to the exterior free end portion of an adjacent tubular element by the method disclosed in the aforesaid '210 patent. The arrangement is such that when the movable component of the hand piece is manually moved from a closed position to an opened position, the free ends of the tubular elements of the stone extracting unit are moved radially outwardly with respect to one another by virtue of the wire elements moving outwardly of the free ends of the tubular elements while their free ends are connected to free ends of adjacent tubular elements.
An advantage of the “N-Gage” device is that it can be used to capture stones (1) in the kidney, in which case entry of the stone is through the open center defined by the wire elements backed up by the diverging tubular elements or (2) in the ureter, in which case entry of the stone is between spaced apart backup tubular elements.